Operational excellence today is a key management theme for each and every organization. Operational excellence has its genesis in manufacturing dating back to the pre-Industrial revolution. The Postal history in Kenya dates from the early years of the 17th century. This study aimed to establish challenges influencing operational excellence at Postal Corporation of Kenya. The study had a sharp focus on Postal Headquarters in Nairobi. Data was collected from the top management that is composed of general managers in charge of departments. This research used a descriptive research design. The target population constituted of 132 senior managers heading different departments and sections at the corporation. Questionnaires were administered to selected employees of PCK. An introductory letter enabling the researcher to collect data was obtained from JKUAT Nairobi campus. Data was processed before analyzing, for checking completeness of the questionnaire, sorting and coding appropriately. Information was then fed in a computer software programme the SPSS, a data base was created then data entry followed. Qualitative data was analyzed using both descriptive and inferential statistics. Data was presented in tables only. The study findings established that there is a significant positive relationship between organizational structure, organizational culture and operational excellence. The findings also indicated that organizational structure followed by organizational culture influences operational excellence in Postal Corporation. The study noted that organizational structure to be the major contributor towards realization of increased operational excellence in Postal Corporation. Organizational structure determined the uniqueness and competitiveness of organization products in the market and this played a key role in determining the state of operational excellence.